Hydrothermal Doping of Nitrogen in Bamboo-Based Super Activated Carbon for Hydrogen Storage

Abstract

N-doped microporous activated carbons were synthesized by hydrothermal doping with ammonia as the nitrogen precursor; the chemical, structural, and hydrogen storage properties of the developed activated carbons (ACs) were also examined. The results showed that this method is an effective way of preparing microporous activated carbons with high surface area. Both the surface areas and the N contents of ACs were increased after hydrothermal doping, and hence, the hydrogen storage capacities were improved. The hydrogen storage capacity of the N-doped ACs was 3.10 wt.% at 77 K and 1 bar, showing an enhancement factor of 1.13 and corresponding to the NAC with both highest surface area (3485 m 2 /g) and N content (2.2 wt.%). Statistical analysis showed that both the N content and surface area had positive contributions to the hydrogen storage, and it also could be predicted by the linear model from the N content and surface area. These results were among the best in hydrogen storage carbon materials, and the high hydrogen storage capacities were attributed to the high surface area.

Cost-Effective Monolithic Hierarchical Carbon Cryogels with Nitrogen Doping and High-Performance Mechanical Properties for CO2 Capture

“…The initial Q st values at a low adsorption quantity of 0.1 mmol/g or at the beginning of the adsorption is 35 kJ/mol (when <20 kJ/mol, physical adsorption alone). This value is much higher than the enthalpy of liquefaction of CO 2 (17 kJ/mol) and porous carbon materials, even some nitrogen doping porous carbon materials. ,,,,,, The results indicated that the surface of the PMF carbon cryogels provides a significant improvement over the affinity of the gas itself and a stronger interaction between CO 2 molecules and carbon cryogels. The main reason for the high adsorption heat is the large number of micropores and the interaction between nitrogen-containing functional groups and CO 2 during the initial stage of adsorption. ,,,, However, it must be noted that these values are still much less than the energy required to dissociate covalent bonds, which suggests an effortless reversible process because of the low-energy consumption for desorption.…”

“…Table shows the S values of all samples, which are in the range of 13–18, indicating that all the carbon cryogels obtained are ideal separation materials of CO 2 /N 2 mixture. This can be explained by the fact that compared with N 2 , CO 2 has greater polarizability and quadrupole moment, and the introduction of nitrogen and oxygen atoms increases the polarity of the material, thereby improving the CO 2 /N 2 selectivity. ,, The adsorption selectivity of CO 2 /N 2 and capacities from these carbon cryogels suggests that it has a higher or comparable selectivity and capacities toward CO 2 than the nitrogen-doped porous carbons from the open literature, ,, which is attributed to the higher surface area, appropriate pore size, and heteroatom doping also. However, it should be mentioned that this CO 2 /N 2 selectivity is still lower than some previous reported results but the CO 2 adsorption capacities are higher. ,,, In addition, to investigate the cyclic stability of PMF-1:2.5, a repeated adsorption test was conducted at 0 °C and 1 bar.…”

“…There are many kinds of porous materials, such as zeolites, activated carbons, − carbon gels, − and metal–organic frameworks. , By contrast, carbon gels are more popular because of their unique three-dimensional network with controllable pore structure. On the basis of Pekala’s work on organic aerogels from resorcinol formaldehyde resin in the 1980s, the resorcinol is a highly cost activity and is not conducive to industrialization.…”

“…It is well-known that CO 2 adsorption on carbon materials is mainly physical adsorption, and its adsorption capacity must be related to the pore structure, which has been studied extensively. ,, Moreover, it is well-known that heteroatom doping, particularly nitrogen doping, is considered to be an effective method for improving the CO 2 capture performance of porous carbon materials. ,,, The inclusion of nitrogen can change the surface chemical properties of carbon materials, which has a certain impact on the CO 2 adsorption capacity and selectivity. ,,,, At present, there are two main ways to dope nitrogen into carbon materials, namely, carbonization of nitrogen-containing precursors and post-treatment with nitrogen resources. , However, the latter is found have lower application value due to nitrogen shedding during later use and pore blocking caused by the post treatment process. , Melamine can be used as one of the raw materials for the polymer synthesis, and the latter can be further used as nitrogen containing precursors to produce N doping carbon materials. ,, Khalid et al reported a carbon cryogels from melamine formaldehyde resin but restricted by the very low surface area (88.44 m 2 /g) and carbon yield (<5%). Zhang et al reported a melamine–starch–formaldehyde organic aerogels with good mechanical properties, but the corresponding carbon aerogel has not been investigated.…”

Discussion About Carbon-Based Solid-State Hydrogen Storage Materials

“…Compared with previous studies, N-doped activated carbon (NAC) demonstrated the best H2 uptake property. [10] Later a 2019 study reported a Pt-N-doped AC with further improved H2 uptake improved. Meanwhile, they also found that the porous structure mainly dominant the H2 uptake ability at traditional 77 K temperature, while the Pt content started to proportionally correlated to the H2 uptake at 298 K. [11]…”